The present invention relates to an improved sheet metal structure, and more particularly to an improved cowl damping structure for use in the combustion chamber of a gas turbine engine.
In a combustor of a gas turbine engine, guide vanes direct pressurized air from the compressor. This air moves over the inner and outer liners of the combustion chamber, or combustor, to provide a cooling effect. Gas turbine combustors generally require a combustion cowl for dividing the incoming air into the primary zone dome flow and into the upper and lower combustor annulus air flows. The impinging air from the compressor exit causes the cowl to vibrate mechanically, which leads to high cycle fatigue of the cowl.
In the existing art, a formed sheet metal part is rolled on a forward end to encase a continuous damper wire. Typically gaps or spaces exist between the formed sheet metal part and the damper wire where they are not in contact with each other. The locations where the components are in contact with each other produces a sliding friction force between the wire and the sheet, which dampens the vibration force. Over a long time exposure, the wire-damped cowl having such gaps experiences typical wear problems associated with friction damping systems. The wear causes thinning of the sheet metal that leads to a shortened part life, requiring frequent replacement of the combustion cowl.
It would be desirable, then, to improve the cowl damping structure in a gas turbine combustor, by improving or increasing the contact area between the damper wire and sheet metal to reduce the wear rate of the combustion cowl.
To improve the existing cowl design, a cowl wrap wire process is proposed. The manual spinning process of the existing art is eliminated, and replaced with a controlled die-form operation and heat treat. The heat treat will occur after the first curl of the sheet metal around the wire. After heat treat, a final controlled die-form process is applied to close the sheet metal around the wire. This yields a consistent contact area around the part that is greater than the contact area using the existing art process.
In one embodiment of the present invention, a method for increasing contact area between a damper wire and sheet metal component in a combustion cowl of a gas turbine engine is provided. The method comprises of several steps that include the following. Processing a sheet metal component having a forward diameter at a forward end and an aft diameter at an aft end wherein the forward diameter is smaller than the aft diameter. Placing or situating a damper wire onto the sheet metal component adjacent to the forward end so that an area of contact is created between the damper wire and the sheet metal component. Die-forming a first curl in the sheet metal component around the damper wire prior to heat treat to create a cowl wrap wire structure. Applying a heat treat operation to the cowl wrap wire structure to conform the sheet metal component and the wire thereby increasing the area of contact between the damper wire and the sheet metal component. Then die-forming a final curl in the sheet metal component around the damper wire in the cowl wrap wire structure after heat treat to create a combustion cowl.
In another embodiment of the present invention, a combustion cowl for use on a gas turbine engine is provided. The combustion cowl comprising a sheet metal component, a damper wire, and an area of contact between the sheet metal component and the damper wire. The sheet metal component having a forward diameter at a forward end and an aft diameter at an aft end wherein the forward diameter is smaller than the aft diameter. The damper wire on the sheet metal component is adjacent to the forward end. The area of contact between the damper wire and the sheet metal component is increased by applying a first die-forming operation, a heat treat operation, and a final die-forming operation after the heat treat operation in order to curl the forward end of the sheet metal component around the damper wire.
Accordingly, the present invention provides an effective technique for improving the contact area between the damper wire and sheet metal to reduce the wear rate of the combustion cowl.